Question

How many moles of h2o are produced when 64. 0 g c2h2 burn in oxygen?.

Answer 1

Balance the combustion reaction:

a C₂H₂ + b O₂   →   c CO₂ + d H₂O

Count the atoms on both sides of the reaction:

• C : 2a = c

• H : 2a = 2d

• O : 2b = 2c + d

Let a = 1; then c = 2 and d = 1, and it follows that

2b = 2•2 + 1 = 5

so that b = 5/2, and the balanced reaction is

1 C₂H₂ + 5/2 O₂   →   2 CO₂ + 1 H₂O

or, with integer coefficients,

2 C₂H₂ + 5 O₂   →   4 CO₂ + 2 H₂O

C₂H₂ has a molar mass of about 26.038 g/mol, so we have a starting amount of

(64.0 g) (1/26.038 mol/g) ≈ 2.46 mol C₂H₂

According to the reaction, we produce H₂O in a 1-to-1 ratio with the C₂H₂ that is burned up, so we end up with about 2.46 mol H₂O.